Answer: Implantable cardioverter defibrillators, or ICDs, deliver the shock through wires -- that are skinny catheters -- that are placed in the heart. And the shock then is delivered basically within the heart chamber itself, rather than over electrodes that are placed on the skin on the chest. These are exceptional devices. They have an accuracy of 99 percent reliability -- 99 percent -- and they have saved an untold number of lives.

We implant them in patients who are at risk for having a life-threatening heart rhythm problem, either a survivor of a such an abnormal heart rhythm problem, or we can identify patients who are at risk for having sudden death and can implant this device prophylactically.